Block coupler



R. P. BOYER, JR 2,686,841

`BLOCK coUPLER 9 Sheets-Sheet l Aug. 17, 1954 Filed 06t- 13. 1950 R. P.BOYER, JR 2,686,841

Aug. 17, 1954 Aug. 17, 1954 R. P. BOYER, .1R

BLOCK COUPLER 9 Sheets-Sheet 5 Filed Oct. 13, 1950 (NNN INVENTORTRICHARD P. BOYER JR. BM 9 `ATTORNEY WAug; 17, 1954 R. P. BOYER, JR

BLOCK COUPLER 9 Sheets-Shet 4 mmm oww INVENTOR.

RICHARD P. BOYER JR. SYM Q.

v ATTORNEY Filed Oct. 13, 1950 Aug. 17, 1954 R. P. BOYER, JR

BLOCK COUPLER 9 Sheets-Sheet 5 Filed Oct. l5 1950 KMJJOIFZOU 9Sheets-Sheet 6 INVENTOR: P BOYER JR BLOCK COUPLER R. P. BOYER, JR

AT TORNE Filed Oct. 13, 1950,

Aug. 17, 1954 rznm ozoSo omom R. P. BOYER, JR 2,686,841

BLOCK coUPLER 9 Sheets-Sheet 7 am ism il Aug. 17, 1954 Filed oct. 1:5,195o Aug. 17, 11954 R. P. BOYER, JR

BLOCK COUPLER 9 Sheets-Sheet 8 Filed Oct. l5, 1950 UCI-m- INVENTOR:RICHARD P. BOYER JR. BYa/yy J. W7 ATTORNEY Aug. 17, 1954 R. P. BOYER, JR2,586,841

BLOCK lcouPLER Filed Oct. 15. 1950 9 Sheets-Sheet 9 FIG. 4

FIG.3

FIG. 2

PART 3 FlG. 6

F IG. 2

PART I FIGJ INVENTOR= RICHARD P. BOYER JR.

AT TORNE to close UNITED STATES PATENT OFFICE BLooK ooUPLER Richard P.Boyer, Jr., by mesne assgnmen phone and tion of Maryland La Grange,Ill., assigner,

Telegraph C ts, to International Teleorporation, a corpora- ApplicationOctober 13, 1950, Serial No. 190,030

I. GENERAL DESCRIPTION The improved block coupler of this invention isl`a direct improvement aftertermed the former application or disclosure.l i

Except as hereinafter pointed out, the system using the improved blockcoupler may be as disclosed in 'the said former application.

As in the former application, the block-coudigit dialed following thedialing of the units digits.

Specic features of this invention include the following:

the transmission (2) The sequence device, which distributes the Yextended thereto, from accomplished by using a charged electrolyticcon-A denser tosupply the required flow of neutralizing current.

(4) Thestepping action of 'the sequence de- (5) The input wires of thedigit counters are a common point, through respective rectiers, therebyreducing switching points otherwise required.

Other specific features include the provision of `lookup contacts on thecoupler busy-key and improvements in the number-transfer andstation-intercept operations.

Additional objects and features of the invention will appear as thedescription progresses.

IA. Drawings The accompanying drawings, comprising Figs.

1 to 8, disclose vention `as follows:

Figs. 1 to 4 taken together show in detail the circuit path andintimately associated electrical equipment employed in extending talkingconnections from a calling line to a called line by way of a line-linkand an -originating 'trunk on line-link frame A (Fig. 1), block coupler`500 (Fig. `2, parts 1, 2, and 3), a block-link and a on the block-linkframe (Fig. 3) and the line-link of line-link frame B (Fig. 4)containing lthe called line. Fig. 1 shows apparatus on line-link frameA; Fig. 2, parts 1, 2, and 3, show circuit details of the block coupler;Fig. 3

the block-link frame; paratus on` line-link frame B Figs. 5 and 6 show asecond embodiment of the invention with Fig. 5 comprising the modiredFig. 7 shows the way in which the sheets of drawing on which Figs. 1 to4 are drawn should be arranged in order to be understood best.

' way the sheets of drawings on 6 are drawn should be arranged morder tobe understood best.

`The devices shown at SE, IDR, HR, TR, UR, and SR (Fig. 2, part 3) aremagnetic impulse general type dis--` Patent 2,441,001, issued May 4,`1948, but are disclosed, withminor changesin preferred embodiments ofthe in- Filed Serial No.

711,111 NOV. 20,1946. 48,008 Sept. 7, 1948.

II. GENERAL 'OPERATION The operations involved inextending a 'talkingconnection from a line such as 200 to a -trun'k such as 2020 extendingto exchange C or to a line such as 2|0 will now be described generally.

IIA. Station S1 calls station S2 The subscriber Aat station Si on Aline200., '.to call the subscriber .at-station-'S2 on line 12410, .removeshis rreceiver, waits for :dial tone vfrom a local block coupler; andthen dials the directory number of staton 5S2, 'containing five digits,termed initial, hundreds, tens, units, iand :stations.

When :the vreceiver is removed at calling -station Si, calling line 200is thereby bridged in the usual manner 'to operate the usual line relaythereof. results in GOIl'tIDllei Switches vldtlllA and l NBA toassociate line controller |200A with line-link yprimary switch 000A at'which thecalling line terminates. The line links (such `as 202A)serving primary switch 800A are thereupon tested Aby the `linecontroller 212A, and I'the associated :originating trunks, -such as203A, are tested over 'respective 'conductors 2|3A. From these tests,the line controller matches an idle path for extending the calling line-to an idle block coupler, the `path over linelink .202A and originatingtrunk 203A, for example. When this occurs, the line controller causes`primary and secondary switches `ililll and SOA'to effect a mechanicalselection of the matched line link 202A, and energizes Aconductorsv 211A.and 2|3A Ato vclose the appropriate stackups of contact elements in theprimary and secondary switches 800A and 900A to extend the calling lineover line link 202A to the block coupler 500., to which originatingtrunk 293A is connected by jumper 204. Line-controller switches 000A'and H'UEA, and line controller 1200A are `now returned to common use,leaving the .calling line 200 connected to block coupler 500, by way ofline link 202A vand originating trunk 203A.

Upon receiving 'a vdial-'tone signal over the established connection,from block coupler 500, the subscriber at calling station S1 operateshis usual calling device to transmit impulses representing the fivedigits in the directory number of called stations S2. They comprise aninitial digit indexing the desired exchange, and hundreds, tens, units,andstations 'digits indexing the called line and the called .station `S2thereon. 'These Adigits are recorded .on .respective `registi-:nrs in.block .coupler 1500 before any external 4switchboard action occurs. Assoon as the stations digit has been dialed, `blockf-controller switch|500 associates block controller |1600 ywith :the primary switch :|300-which serves block coupler 00. At the same time, block :coupler 500 isassociated with block `controller .|000 over the Aconductors :in `group22|.. Also, atthe the operation of line-- |200A over respectiveconductors` information 4 same time, the dialed hundreds, tens, units,and stations digit information is transmitted to block translator |800over the conductors in group 220. The block translator thereupondetermines the line-link frame which serves the called line (ilinelink.traine A25013)., -and transmits thereto (over lconductors in group223B) translated digit indicating the primary switch 168MB) which servesthe called line, and indithemselves .according to the such as .206, a

rover #conductors 4iin group eating .the specific vertical appearance ofthe called `line on that primary switch. When this occurs, .linex'controller |200B identifies itself at block controller |1500, andexercises a control 240B to cause lineand ||00B to position switchboardlocation oi the called line. The line links (such as 202B) lservingprimary switch 800B are now tested over respective conductors 2|2B, andthe testing information is imparted to :block Sconcontroller Lswitches|000B troller 4.0.00 over respective vconductors in group- 222B. Thesleeve conductor 2|1:|'B of the calledl line 21.0, is .now extended toblock lcontroller A|1000 over a conductor -in `group block controller totest the called line to determine its busy or idle condition.

If thefcalled line tests idle, the blockcontroller matches zan idle paththereto over va block link terminating trunk such as 201B, and -a linelink such as 202B. .The block and terminating trunks are tested overrespective :conductors 2.25 and 22E.

When this available idle path .between blocky coupler 500 and the calledline has been determined, block controller |600 closes appropriateselect-magnet circuits to effect ymechanical selection of yblack link.206 at primary .and secondary switches |300 and |400, -and to effectmechanical selection of line link 202B at 'switches 900B and 800B. Whenthese .selections lhave been made, block controller |600 operatesthrough :a `conductor in group 22| to close the appropriate circuit paththrough primary switch |360 fto -extend .the vconnection to the selectedblock-.link 205; operates over rconductor 1226 to cause the appropriate'connection to be closed in secondary .switch |400 to extend block-link-206 to Iterminating trunk 201B, and to cause that trunk to ybe extendedto 'the selected line :link 202B by 000B, `and operates, over aconductorin group "222B, and over sleeve conductor 2| IB, to cause theappropriate connection `to be closed in primary switch 800B tointerconnect line link 202B with the vcalled line 2|0.

Upon the foregoing operations having been completed, local block coupler500 begins to apply ringing 'current to the called line to signal thecalled station S2 thereon over the established connection across theyblock-link frame and across the called line-link frame, and the itemsof common Aapparatus (block-controller switch |500, lblock-controller|600, block translator i800, and line-controller apparatus 1000B toV|2|liB are promptly returned to common use, leaving the connectionintact between the calling Aand called lines.

When the call has been answered, the subscribers at Ystations Si and S2may converse.

When both subscribers have replaced their` receivers, .block coupler 500opens iront and rear holding circuits which it had previously heldclosed, whereupon the existing connection is broken at yeach vof theswitches 000A, 900A, |300, |400, 900B., and 800B.

222B, enabling the links.

nn. staiionsi `callsecclnm'ge` ci f When the Subscrberat station si on1in`e"zno desires to call a s` receiver; waits for dial tone; and thensubscriber 'of exchangeC, he retolines `of exchange C..

Whenjthe receiver is removed at call station I,

and originatingtrunk 203 when the initial digit assigned speciiicniiy toexchange C1 is pler 500,

15 dialed and recorded in block couav connection is immediatelythereupon completed over a Wire in initial digit group ID for calling inoutgoing controller` |100 `and for setting 20 coincidentally with theassociation of block coupier son withV biock continuer |600 `overconductor group 22|; and `withthe operation of block-controller switchassociate block i controller switch |300. going controller aref boththus the block controller is adapted tend the connection to an idletrunk in the called |500 over conductor 'group 224 to 25 600 withprimary controller and outcalled in' together,

specifically to exwiien the block outgoing group. The circuitarrangements are such that `the operations necessary to cause theextension to be made occur with sufcient rapidity that the callingsubscriber introduce `an additional delay to call the remaining digitsin is not required t0 before proceeding the desired telephone number;

If block link 206 and outgoing trunk 2020 are both idle (as shown bytests made over respective conductors 225 and `221) block controller|600,

taking into account information imparted thereto over conductors ingroup 24|, may select that path andi condition switches |'300and |400toselect block link 20B mechanically. Thereupon,

block controller |600 points to be closed in causes appropriate crossswitches |300 and |400 t0 vinterconnect block-coupler extensionconductors 205 with outgoing-trunk conductor202 by way of block link206, thereby extending the calling line through block coupler 50,'totrunk coupler 200| on frame trunk-extension V2023 252,` and thence`through and` jumperp2|i24 to thel trunk conductors outgoing toex'changeC.' `When thisoccurs, block coupler 500 switches through as will behereinafter explained, andthe connec-` tion from the calling line to theoutgoing trunk is thereafter held by trunkwcoupler 200|, which couplerincludes apparatus for repeating the succeeding digit impulses over thetrunk line to apparatusinexchange C; -Coincidentalwith the` switchingthrough operation `noted for `the block coupler, the items ofcommoniequipment' on the block-link frame (block-controller switch |500,`block controller |600, andjoutgoing controller |100) are disassociated`fromfthe` estab,- lished connection and arefreturned to, common Theconnectionl established fromthe calling line to the` outgoing trunlr` isreleased responsive to operations occurring in trunk coupler 200| Whenthe receiver calling station Sl. i

is subsequently replacedat the 70 IIL FIRSTnMBonnvinirrp(Eros:1` To 4) iThe oper will now b ation of the system incompletingcalls described.This partoftlie descrip'- 75 chain. tof

61 tion covers in complete detail the operationeel the `portions of theapparatus directlyvincluded IIIA. Block couplerl 50o As shown in Fig. 2,parts 1, 2*, and 3, local block oupler 500 includes a test 5 I8,condensers 5|9 to 524, rectiflers-EZB to 53|, resistances 532 to 542,and `magnetic counters SE, IDR, HR, TR, UR, and SR.`

IIIAl. Circuit functions of coupler 500- i i Local block coupler 500principal circuit functions:

(1) Normally, it supplies idle-indicatingbatl tery potential to thesleeve conductor of itsat-` tached originating trunk.

(2.)l On all calls: 2a; Upon seizure, 'the calling line untilthe firstdigit (other than 1) is dialed and (2) removes the idle-indicatingbatconductor of its holding ground potential. 2b. If the start ofdialing is delayed for the normal time-out period (about two to fourminutes), it times out by removing holding ground from the sleeve of theattached originated trunk to permit release and lockout to occuron theline^ link frame. i

`2c. It absorbs the initial digit 1 as many times as dialed or otherwiseproduced.

(3) On an outgoing call: i

3a. It receives and stores a single digit forf transfer to the outgoingcontroller.

` 3b.` It temporarily seizes the outgoing chain of its localblock-coupler section, subject to such A cham being idle, and thereafterguardsthe seized` 3c. It transfers the sin outgoing f chain. i

3d. On a signal from the block controller that no idle path can be inthe calledgroup, calling line, chain.

it (1) applies a busy tone to 3e.` On a hold-pilot signal from the blockcontroller `that the connection has been in4 the called group, it (l)switchesthrough to the and (2) frees the seized outgoing 4b. If thedialing or answeringis `delas/'ed period, it times out as pre" thenormal time-out viously noted.

impulse it (l)` applies dial tone to gie stored digit in the outgoingcontroller incident to seizure of the` matched to an outgoing trunk 1and (2),` frees the seized outgoingV such ground is removed. l

tothe outgoing controllen tens digit T, a units digit U," ST `fortransfer to the block' accessi 4d. It transfers the rive digits ofstored digit information to the .outgoing controller and to the block:translator while it has the terminating chain seized.

4e. On a signal from the block controller that the called line is busy,or that no idle path theretocan be matched, it (l) applies a 'busy `toneto the lcalling line, and (2) frees the seized terminating chain.

4f. 0n a hold-pilot signal from the associated vertical of theblock-link primary switch that the connection has been extended over amatched path to the called line, it `(l) applies ringing current to thecalled line, (2) applies ringing tone to the calling line, and (3) freesthe seized termin atng chain.

4g. When the call is answered, it (l) trips the ringing circuit; (2)completes the talking connection; and (3) reverses the current flow overthe tip and ring conductors of the attached originating trunk, subjectto hookswitch control from the called line.

4h. It supplies transmitter current to both lines.

. 4i. If the connection is still held by at the end .of the timedconversation period (about eight to ten minutes), it times out aspreviously noted, but applies a warning-tone pulse of busy tone currentto the connection about half a minute earlier.

41'. If the connection is still held by the calling line after thecalled vline is opened, it times out at the end of the normal time-outperiod.

4k. Whether the called line is still closed or not when the calling lineis opened, it clears out and releases the entire connection, by removingholding ground from the incoming sleeve Vand from the sleeve of theforward connection.

(5) On a reverting call (wherein the calling subschiber dials theregular directory number .of the called subscriber):

5a.. It functions as stated in the foregoing items 4a to 4d for a normallocally terminated call.

- ,5b. On a lsignal from the block controller that the call is areverting call (a call going back to the calling line), it (l) applies areverting-call tone to the calling line, and (2) frees the seizedterminating chain.

5c. When the receiver is replaced on the calling line .in obedience tothe reverting-call signal. it -(l) locks itself to hold the connection,and (2) sends ringing current back over its associated originating trunkto the calling line.

5d. When the reverting call is answered, it unlocks itself and clearsout, removing holding ground from sleeve of its associated originatingtrunk to permit release and lockout to occur on the lassociatedline-link frame.

IlIAZ. Relay functions of cowpler 500 The eighteen relays (501 to 518)of block coupler 500 have principal functions assigned thereto asfollows:

n Relay 501 (switch-through) switches the incoming trunk conductorsthrough metallically to the outgoing ones on outgoing calls andreverting calls. v

Relay '502 (back-bridge) operates over the called line, when a locallyterminated call is answered, to reverse the incoming tip and ringconductors under control of the-hookswitch on the called line, and toprevent normal time-out from taking place during conversation.

Relay 50.3 (line) operates when the coupler is seized, and restoresthereafter, under control of both lines the calling device forhookswitch, whenever the calling line is opened.

Relay 504 (hold) is 'slow-releasing, by virtue of a copper sleeve underits winding; ,is operated by the line relay; and remains operated.during pulsing, but releases when the line relay remains restored for asubstantial fraction of Va second.

Relay 505 (hold-auxiliary) is operated when the coupler is preliminarilyseized; it places a holding ground potential on the sleeve conductor ofthe attached (originating trunk; it normally releases when the holdrelay releases; .and it `operates the knock-down relay to restore allcounters to normal.

Relay 506 (time-pickup) is operated as re' quired, to start the finalportion of .a normal timeout period or of the conversation-time periodtorender a connection :subject to release by the common timing apparatus.y

Relay 501 (ring-pickup) is operated -on locally terminated calls tocomplete a path for ringing current to be placed on a called line.

Relay 508 (ring-trip) is operated by direct current flow when the calledline `answers in order to terminate ringing.

Relay 509 (ring-reverse) is operated from the block translator on anystations digit 5 to 9, to cause ringing current to be applied to theother side of the line for divided ringing.

Relay 5 I 0 (ring-cutoff) -is operated by the ,ringtrip relay when thecall is answered, to open the ringing circuit and to close the talkingcircuit.

Relay 511 (series) is slow-releasing by virtue of a copper sleeve underits winding; it isr operated by the line relay at the beginning of each,series of impulses; it remains operated during each such series; andreleases at the end :of `each series to operate the sequence counter.

Relay 512 (reverting-call) is operated .by :the block controller tocondition the block. coupler for a reverting call.

Relay 513 (switching) is operated when a locally-terminating connectionis extended to the called line; to free the seized terminating schein;to close the ringing circuit; and the like.

Relay 514 (busy) is operated from the block controller to applybusy-tone signals .to the calling line.

. vRelay 515 (outgoing-chain) is operated on an outgoing call when thesingle outgoing digit has been dialed; it seizes the .outgoing chain ofthe local block-coupler section for the exclusive ause of this blockcoupler.

Relay 515 (terminating-chain) is operated on a locally-terminated callwhen a station digit has been dialed; it seizes the terminating chain onthe local block-coupler section for the `ex clusive use of this blockcoupler.

Relay 511 (knock-down) is operated when the calling line disconnects ordials the initial digit l, to release all operated counters.

Relay 518 (transfer) is operated Aduring the ringing period to transferthe tens leads controlled by station register SR, from the station leadsassociated with the block translator, 'to the ten interrupted-generatorleads.

IIIA3. I nantaise-counter functions of coupler `500 The six impulsecounters (SE, IDR, HR, TR, UR, and SR) of block coupler 500 haveprincipal functions assigned thereto as follows:

Impulse counter SE (sequence device) responds to the release of seriesrelay 511 at the lend of each digit series of pulses to .distribute theseries of .digit impulses to registers IDR to SR.

:.-Impulse counter IDR (initial-digitregister) registers the number ofimpulses in-the'rst digit dialed, the initial digit. p I n Impulsecounter HR (hundreds register) registers the number of impulses in thehundreds digit.

Impulse counter TR (tens register) registers the number ofimpulsessigned to impulse counters device SE,

tion and takes timed steps 6 to 9 incident to conversation timing.

`Initial-digit register lead, and also controls tial digit l. IIIB.Locally-originated calls The operations involved in makinglocallyoriginatedcalls from station SI on line 200 will now be describedwith reference to Figs. 1 to 4.

` IIIBI. Initiation of cazz When the receiver (not shown) is removed atcalling station SI of Fig. 1,

IDR opens the dial-tone the absorption of the inimay be assumed tobeover `line link 202A to originating trunk 203A. The test circuitfor linelink 202A from line controller 1200A is from line-test idle indicating.battery potential ony the sleeve of the link, which is supplied throughthe illusbattery wire LB,` and contacts of one of the linecontrollerswitches. If line link 202A is ibusy, holding ground potential thereonmarks the resistance-supplied battery potential, `causing the link totest busy, but the idleindicating `battery potential is eiectivelyreceived bythe linecontroller vwhen the line link is idle;

1 When originating trunk` 203A (being connected to block coupler 506through jumper 204, Fig. 2, part 1) is idle, the line controller I200Areceives an idle indicating battery potential over matchtest conductorMT-2I3A break contacts on test jack TJ, break contacts A of switch relay5I3, break contacts IA of sequence counter SE, through potenti-al.

Upon matching a path over line link 202A to originating trunk 203A, linecontroller I200A circuit through troller switches for primary and 405whichare contacts of one of the line-conand over select-magnet wire SMsecondary selectmagnets 404 and associated with the primary end PON andcontacts of one of the line-controller switches to the primary-secondaryoil-normal wire PS-ON leading to the line controller.

Upon receiving battery tacts of one of the line-controller switches tosleeve conductor S-ZI IA .(an extension of sleeve trated hold-pilotcontacts HP to disconnect line relay 40| (in the manner ofthe usualcutoff relay), whereupon line relay 40| restores.

Lockout relay 402, upon operating in series with hold magnet 403,prepares for placing the associated line in lockout condition if calledupon to d0 SO.

magnet 403 and 406 closed for an interval `sufcient to permit the seizedblock-coupler 50Il=to accesar return holding ground over the sleeveconductor IIIB2. Preliminary seizure of block-coupler 500 As noted, theoperating ground applied to hold magnet 406 is also applied tohold-auxiliary relay 505 causing it to operate. Make-beiore-breakcontacts 2 oi relay 505 places a holding ground from contact 1 ofterminating-chain relay 516 to the sleeve conductor of originating trunk203A to maintain hold magnets 406 and 403 operated when the linecontroller 1200A clears out as previously noted. Preliminary seizure ofthe blockcoupler avoids any trouble which might arise with a relay suchas relay 503 (line relay, Fig. 2) being in parallel with another relaysuch as relay 401 (line relay, Fig. 1). If these two relays are inmultiple on a long line,v sufficient current is supplied for theoperation of one relay but not for two.

When the described extension of a connection from. calling line 200 toblock-coupler 500, over line link 202A, originating trunk 203A, andjumper 204, is completed, line relay 503 operates over the. calling linethrough break contacts 1 and 2 of relays 501 and 502. Line relay 503, atits contacts 1, operates hold relay 504 from ground` at back contacts '1of switch through relay 501.

At itscontacts 4, relay 504 extends ground from break contact 4 oftime-pickup relay 506 as a holding ground for relay 505 when linecontroller 1200A clears out. The established connection, from. thecalling line to the block-couplerI 500, is thereby maintained after theline-controller apparatus of Fig. tacts 1,. hold relay 504 extends aground through resistance 535 to the winding of switch-through relay50.1 to partially energize this. relay. Relay 504 at its contacts 2,prepares an operate path vfor series relay 511 through break contacts onrelays 513, 514,. 510, and 51:2.

Hold-auxiliary relay 505 at its contacts 1 place ground on the machinestart lead; at its contact 5 prepares the operate circuit for knock-downrelay 5111 by discharging condenser 522 through resistance 532'; at itscontacts` 4 it prepares an operate circuit for the sequence register SE'under control of contacts 2 of series relay 511 by transferring normallycharged condenser 523 to w-ire 555, and at its contacts 3 places aground on locking wire 560. At its contacts 6, relay 505' extends d-ialtone through break contacts 1 of initial digit register IDR, contacts1.1 of relay 513, contacts 5 of revertingcall relay 512, through breakcontacts 0 of ring cut-oft relay 51'0 and through small-capacitytone-coupling condenser 521 to the tip of the calling line.

IIIB3. Receipt of digit-pulses` On hearing the noted dial-tone. signal,the calling subscriber dials the digit in the directory number of thecalled line or station.

Each time the calling device is operated to transmit a series ofcircuit-interruption impulses, line relay 503 is restored momentarilyfor each such interruption impulse in a series, comprising from lto l0impulses, depending on the digitv dialed.

Relay 504 remains operatedV and maintains relay 505 operated (contacts4)l throughout any series of impulse-induced restorations of line relay503, relay 504 being slow-restoring because of' its indicated coppersleeve.

Series relay 511 operates promptly upon the first restoration of lineVrelay 503., its operate path being as` follows: Ground on back contacts'1 of relay 501 is extended through pulsing contacts 1 of line relay 503,make contact 2 of relay 504, break contact 10 of relay 513', breakcontact 4 of relay 514, break contact 5 of relay 51.0' and break contact4 of relay 512. to battery through the winding of relay 5.1.1.. Relay511', being slow--4 releasing becausev of the indicated copper sleeveunder its winding, remains operated throughout the digit series ofmomentary restorations. of the line relay. At itsA contact. 2, relay51:1 discharges condenser 523 through resistance 536' prepa* ration foroperation of the. sequence counter SE as will hereinafter be described.

With hold relay 5014i maintained continuously operated as noted,restoration of line relay 503 delivers an impulse at its break contacts1, through make contacts 2 of relay 513., break contacts 10 of relay 513and break contacts 4 of relay 514 to impulse wire 550. Thedigit-sequence contacts, sets 1B and 2 to 5 of sequence counter SE areso inter-connectedthat the iii-'st series of impulses over wire 550 istransmitted to the winding of initial-digit register IDR.

Whenv line relay 5.03v comes to rest, operated at the end of any seriesof impulses, series relay 511 shortly releases responsive to theopeningv ofits. operating circuit for a period of' time great.- er thanits hold-over time, and closes a stepping circuit. for sequence counterSE. f

When relay 51 1 releases at the end of the first series `of digitimpulses, its contacts. 2 transfer condenser 523 from resistance ground(resistor 536) to battery through contacts 3 of relayv 511 and thewinding of sequence counter SE. The plates of condenser 523, havingunequal potentials, cause charging currentv to flow through the Windingof counter SE until the condenser is completely charged. This chargingcurrent gen.- erates a stepping impulse for counter SE which causes itto shift its contacts 1A and 1B to their alternate position.

Make contacts 1A of counter SE preparev the clearout circuit. for alloperated counters provided. the; initial digit dialed is the numeral 1;,its break contacts 1A are. opened to preventy the reapplication oiidle-indicating battery toA the incoming sleeve conductor of the coupleruntil. sequence counter SE is. cleared out; break contacts 1B ot counterSE disconnect the incoming impulse wire 550 fromv the digit registerIDR; and its make contacts IB-transfer this wire to thehundreds registerHR.. f On subsequent steps of (whichv occur during reverting calls), itscontacts 2 operate to transfer the impulse wire 550 to.: tens registerTR; its contacts 3 operate to.y transfer wire 55.0 to units. registerUR; its. contacts 4 operate to transfer wire 550 toy stations registerSR; and its conta-cts 5 operate to open impulse wire 5,50 and to closean point in thje circuit. of terminating-chain relay 5161..

111134. Initial-digit registration When the impulses oi the initial.digit. are delivered over wire 550v tothe winding of thee initial-digitregister IDR as4 described, the contact sets .(1 tol 10i). of thisregister are. actuatedsucsequencev counter SE or terminating` l-tacts` 2close a `through `contacts L|I operates, 1ts contacts 5 transfer lplate`of `the condenser tothe resistance battery `contacts IA.

the -windings scriber should cessively responsiverespectively to the'impulses of thedisfit. i l

On receipt of the rst impulse at IDR, its break contacts I disconnectdial-tone lead DT to prevent reapplication of dial tone. `The second im-`control of the counters since the initial-digit is greater than 1, andits make conwire ID2.

i Subsequent impulses delivered to register IDR actuate respectivecontacts to position the register on the initial-digit lead (ID3 toIDIO) which corresponds to the initial-digit dialed.

111135. absorbing the initial-digit 1 Block coupler 500I is arranged toabsorb the initial digit 1 as many times as dialed or otherwiseproduced, as by improper hookswitch operation or by line trouble.Accordingly, the digit 1 is unassignable as an effective initial digit.

uiWhen` the initial digit received contains only asingle-impulse, thefirst contact set is the only one operated in the initial-digit registerIDR. Then, when sequence counter SE operates, as described, at the endof the rst series of impulses `comprising the initial-digit, ground fromcontact 3 of hold-auxiliary relay 505 is extended through break contacts3 of relay 5|0, through make contacts IA of sequence counter SE tobattery through the winding of nockdown relay 5|?.

`Relay5|l thereupon operates and at its contacts I and 2 removes holdingground (on wires 556 and 560) from the counters and release all operatedones through their windings, neutralizing any residual magnetism.

With relay 5I1`in its unoperated condition, condenser 524 is maintainedfully charged from ground (contacts 5 of relay 5I'I) on one plate andresistance battery on the other plate (resistor 534 4 `of relay 5I'I). iWhen relay the grounded `and at thesame time, its contacts 3 remove theother plate from this resistance battery while contactsI and 2 transferit to battery through the windings of the counters through theirrespective current-limiting resistors, 531 to 542. l

`With resistance battery placed on both plates `(resistor 534 on oneplate and the windings of the counters in. series Withtheir respectivecurrent-limiting resistors on the other), and with Ythecondcnser alreadyhaving a positive charge `on one and a negative charge on the other,current ows until both `plates have equal potentials. This condenserdischarging current ows through the counters in the opposite directionfrom which they were originally operated causing all opto release as themagnetic flux generated by the discharging current is in opposiltion tovanyresidual ilux and neutralizes it.

i The release of sequence counter SE opens the operate circuit ofknock-down relay 5II at its When relay 5II releases, its con- ;tacts I,2, 4 and 5 transfer condenser524 from of the counters to battery andground again in order that it again charge in ipreparationfor anotherknock-down operation when; required.` The release of counter SE also4transfers pulse lead 550 back to initial-digit register IDR.` i

-; The release of register IDR reapplies dial-tone -to the calling line`as a signal that the calling substart `dialing from the beginning.

point in the circuit of initial-digit by discharging condenser 524` 14vIIIBA. Outgoing calls` On the dialing of any'initial digit 2 toO,register IDR makes connection with the correspond'-` ing one of the nineinitialdigit leads ID2 to IDI 0, which extend to the outgoing controllerover cable ID. e One of these leads (IDB as illusfto the 100G-line blockof local line numbers, an' is rendered ineiective at the outgoingcontroller". The remaining ID leads extendto the block controllerthrough respective initial-digitrelaysof the outgoing controller `II00and may correspond to respective groups of outgoing trunks.` IIIBAl.Outing call-in of block controller and marking at gronplcontroller` Whenthe initial digit dialed isone assigned to a group of outgoingtrunks,such asthose outgoing to exchange C, the release `of series relay 5II atthe end of the, digit closes the outgoing extend marking ground to the:outgoing |100 over fthe corresponding` one of leads IDI to IDIU. Thisoperation `is subjectfto the outgoing chain being idle, 'in which case aground potential is present on the outgoing `chain-in conductor of thefirst coupler in the block-coupler section containing `the calling'blockcoupler 500. For this section the conductor referred to is OTG-CHIN incable 224 incoming from block-controller switch |500 of Fig. 3. l `Asillustrated and described in the noted former application, thisconductor extends through chain contacts of all of the block-couplers inthis section to the outgoing-chainfend conductor OTG-CIjI-END multipled4the section. `Ground potential on conductor OTG-CH-END now` `passesthrough closed con- ;tacts I` of outgoing-chain relay 5I5, the windingofrelay 5I5, and through break contacts 2, 3, Ii, and8 of relays 5I4,5|I, 50|,` and 5|3,` to wire 55| which leads to register IDR. Withregister IDR set according to an outgoing groupl (such as to exchange C)wire 55| is thereby extended tothe selected one of the initial-digitleads ID2 to IDIO, the one which corresponds to the called group oftrunks. In the noted former application, the outgoing chain circuit isthus extended through a series marking relay in the outgoing controller|100, to battery through the outgoingstart relay of the block controller|6001. The

outgoing-start relayof block controller |0100 and' theseries-markingrelay in the outgoing control,- 1 er |100 mark the called ytrunk group.in the IIIBA2. Chain sez'eure and guarding 4 In the noted formerapplication, the concerned section-preference relay of the outgoingchain relays operates to open the outgoing chain to all otherblock-coupler sections,` `and to position block-controller switch |500to select the blocklink primary switch I300 which serves theblockcoupler section containing the calling block coupler. l i

In the calling block-coupler 500, outgoing-chain relay 5| 5 operates inthe previously traced cir` `cuit to lock itself to outgoing-chamanconductor to all couplers of.

ground` on conductor 560 through '8' of sequence counter SE; opens theoutgoing Il'lBAB. Outgoing-busy condition If no outgoingv trunk in the:called group is available, (as when all trunks in the called group arebusy, or when no.` matchv is possible to any idle. one. of them) or ifan unassigned initial digit has been, dialed,` the block controller |600grounds the common wire OTG-BU (shown as vin cable 221) operating busyrelay M in the block-.coupler through contacts l!y of` relay 515i. Busyrelay 5M at its contacts |V locks itself` to break contacts chain at itscontacts 2V to release outgoing chain, relay 5I.5, freeing the seizedoutgoing chain, the outgoing controller, and. the block controller;opensr impulse Wire 550. at its contacts 4 to prevent. furtherregistration if further digits are dialed.; and at itsV contact 5applies busy-tone to the calling line through make contacts (i oflioldfauxiliary relay 505 and through tone-cou'- Illingcondenser 52|..

, The .calling subscriber is expected to replace his receiver uponhearingI the distinctive busy tone. to thereby initiate the normalrelease of theconnection. Otherwise, the connection times out asis laterdescribed..

IIIBAL. Outgoing matching and path `select-icm v i Normally there is anavailable -idle trunk in the called outgoing group, such as trunk 2020in. which even an idle path is matched to such trunk over a block-link`such asl 206 of the pair 'illustrated in Fig. 3; '2'02'0 is Aindicatedin outgoing controller H00'x by idle-indicatlngbattery potentialnormally applied to .sleeve conductor S of trunk 2020 by trunk coupler200| and reaching the outgoing controller through theK left-hand windingof hold magnet HMH and' matchtest conductor NEP-221i. The busyor idlecondition oi'block links such as 206U and, 2061; is determinedi by theblock controller over'respective sleeve conductors- 225 'f extended'thereto throughcontacts of the block-controller 'switch |500'. Sleeveresistors RU and RL are 4connected respectively to conductors 22 5- byIthe 'block-controller switch, thereby applyingy idle- `indicatingbattery Apotential toeachI of' them subject to being masked by 'ground'potential thereon. at block link which is actually in use.

When the' path over items NEU and' 202 0- has been determined by thematching operation ci" controllers |1500 and H00', block controller|1600 'closes a circuit through contacts of block-controller switch'|500' and over select-magnet wire SM of principal select magnets 505'-'and 60G 'in series. In order to e'ect'selection of the matched upperlink 206U of the illustrated pair, as distinct 'from' the lower link206B thereof, bloel'e controller 'i600 closes a circutfrom ground upperauxiliary select magnet SMU-G04 of pri- The idle condition of trunkthrough the mary: switch |1300v over the .associated wine .SNEEK andcontacts of the block-controller switclccon.- doctors and contactsin.the block controller, wire SMU leading to switch. |4005, and thence tobat'- tery through the upper auxiliary selectv magnet SMU-(i013.AAuxiliary magnets 604 and, 6.0.1: there upon operate tov complete the,mechanicalv selec.- tion of link 200U'.

An. oli-normal. or. pilot. circuit.. now extends from ground throughofi-normal contacts controlled in common byl auxiliary select magnetsalle; and. B04 of. switch |300, contacts: of; any-one of.' the tenyprincip -l magnets; S05-,j primary' olncrmal conductor; PON, contacts.controlled by any one of the ten principal select magnets 606, contactscontrolled in common by =auxiliary select magnets. B01 and. B08, andthenceover seccndary oil-normal conductor SON to block con.- troller|600.`

IIIBA5. Trunk seizure and switch-through l Upon receiving ground' asnoted oyer'the. associated conductor SON, block controller |500 closescircuits to effect the extension. of the connection through switches|3001 and |2400. Closure of the switch |000 is responsive to theapplica..- tion of ground potential' toy match-test conductor MTL-221bythe block controllerithereby clos.- ing a` circuit through theleft-handY winding of hold magnet 609' and' thence over sleeve'conductor` S ot' outgoingA trunk 2020 to batteryv in trunk coupler'20011 Holdmagnet. 609. thereupon locks its right-hand winding'to the.associated sleeve conductor S, at the same time closing its principal'stackup (vertically alignedI with maginet 605) which partially extendsboth blocklinks of the illustrated pair, and closingL its upperauxiliary stackup. U (aligned with'. select magnet lill?)V to extend theconductors T', R, and S', of block link 20ml respectii'felyy toconductors: T, Rs, and Sv of the matched outgoing trunkz2020.

The circuit closed by block controller 1.6002 for effecting closure ofthel matched connection. at primary switch |300 isA over outgoingswitching conductor OTG-SW (shown in cable 22 |:)i, and thence throughcontacts 4 of outgoing-chain relay 515., switching conductor SW, and.thence toA battery throughy the rightfha-nd windingA of hold magnet.Eltville-Q02.r Magnet. GBI locks; its left-hand Winding to ground on theassociated sleeve conductor S? of extension group 205,V and at 'the''same time closes` and auxiliary staclrups selectedI respectively-bymagnets 605 and 604. Conductors T, R, and S, in group 205I are therebyextended respectively to` conductors T, R, and S in block link 20H1,andi then through secondary switch H00'. as stated tothe correspondingconductor in outgoing'trunk 2020..

Hold magnet 602 also grounds hold-pilot wire group. 205', therebyclosing. an1 operate circuit, through break-.contacts of tens: registerTR, for switch-through relay 502| of block. coupier 50.01

Switch-through relay 50| operates: promptly because of its pre-existingpartial energization from ground at contacts ot'- hold relay 50i throughresistance 535. On operating, switchthrough relay 502| opens the closedoutgoing chain at its `contacts 6'-, thereby initiating the clearing outot the common apparatus |5001, |1500, and and restoring outgoing-chainrelay 515.

At itscontacts .I and 2, relay 50| switchesthe 'tip and ring conductorsof the attached4 originatingl trunk through metallically to: conductors.T

its, associated principal weasel.

and R of extension` group 205, now extended across the block link framevto the trunk couslight interval. Hold-auxiliary relay. 595` is releasedat contacts 4 of `hold relay v5cc and removes the local holding groundconnection from the sleeve conductor, leaving the established scrption,thereby releasing counter SE and IDR.

IIIBAS. Outgoing-call clearout Whentrunk coupler 200| clears outresponsive to e receiver being replaced onthe, calling The release ofprimary hold magnet 602, un,- grounds the associated hold-pilotconductor HP The release of switch-through relay 50i completes theclearing out of the block coupler 5 00. At contacts t of relay 50i,idle-indicating battery is again placed on the sleeve conductor.

IIIBB. Terminating calls When following the described seizure of blockcoupler 500, the initial digit` dialed is the digit dserving a .100Gdigit tc index the local block i000 line numbers as described in theformer application, the corresponding initial digit lead IDS (not shownin the Fig. 2, part 3) is selected by initial digit register IDR bybeing connect-ed to conductor 55! through make contact and breakcontact'l (not shown)` ofregister of IDR. Iiead IDE stands open in the`outgoing controller (as`shown in Fig. 17, part 2, of the notedapplication), Wherefore outgoing-chain relay 5l5 is not" operated,` andnone of the common equipe ment is `taken for use at this time.

tacts IB, 2., 3, and 4 respectively of device SE.

Device advances to` position 5 (operate its contacts 5) at the endl of`the registration of thel stationswdigits to` disconnect thecoperating torelease switch-through` relay 50| of coupler l circuit of stationsregister SR; and to call in the block controller.

IIIBBZ. Terminating call-in of block controller ing, and its makecontacts 5 connect up the common terminating-start wire TERFST of theblock controller. If the terminating chain is closed at thesection-preference relays (Fig. 15, part l of the noted application)andis closed at this block coupler section, ground potential through arelay and contacts of the sectioncontacts 5A of counter SE toterminating-start wire TER-ST, shown as a. conductor of cable 22l AsIIIBBS. Chain seizure cmd' guarding Over the above traced circuit, theconcerned section-preference relay is operated to set block controllerswitch i600 on block-link primary operated in a traced circuit, in thisblock: coupler, to seize the terminatingchainto guard it against seizureby any other coupler inthe same section, by locking itself (at` its makeiirst contacts 3) to the associated chain-in Wire, TER-CH-IN, andisolating TER-CHfEND from the. chain at break contacts 3 and 4.

TER-Eliot the bloclrcontroller, and ring-reverse Wire RR of the bloclr`translator.

the registered hundreds, tens, units, and station digits, by groundingleads 552 and 5%, thereby grounding'the previously selected one of theleads of the groups H, T, U, and ST, through respective rectiiers 527,528, 529, and 530. extend to the block translator over cable 220; The

nient. paises-ringing @ammi If any station digit 0, l, 2, 3, or 4 hasbeen dialed, ring-reverse` relay 509 does not operate,

butit is: operated byl the block translator (over I'hese leads ringreverse wire RR as described in the noted former application) if thestation digits information received thereby shows that any station digitto 9 has been dialed. When it is thus operated, relay bili! reverses theringing leads at its contacts l and 2, and at its contacts 3 it locksitself to ground on wire 56|] through break contacts 3 of ring-cut-offrelay 5|0.

IIIBBG. Testing the called Zine As described and illustrated in theformer application, the block translator transmits a suitably translatedversion of the hundreds, tens, and units digits to the line controlleron the line-link frame at which the called line terminates. The stationdigit information is used only for the noted ringing control purposesand for station selection.

If the illustrated station S2 is the one called, it is served by a framewhich includes apparatus shown in Fig. 4. In this event, the translateddigit information is sent to line controller |2'ell5 over conductors incables 223B. Y

On receiving the translated digit information indicating which primaryswitch (primary switch llllB, Fig. 4) serves the line being called, andindicating the fives and units location. of the called line thereon,line controller |2093 identies itself at block controller H500 by asignal transmitted over a conductor in group 222B and positionsline-controller switches NWB and lttB in accordance with line-linkprimary switch SMB and in accordance with the ves group thereon in whichcalled line 2|0 is located.

When switches |000B and IBBB have been set, one of them extends thesleeve conductor S-2| iB of the called line over sleeve-units wireSil-240B to line controller |200B, whence it is extended over aconductor in cable 222B- to the block controller |60@ to enable thecalled line to be tested as to its busy or idle condition. At the sametime, each of the ten link sleeves associated with the called primaryswitch 800B is connected to the line controller through one of theline-controller switches. For example, the sleeve of the illustratedlink is connected through link-sleeve wire LS-2|2B and link-test wireLT. Link resistor LR is connected to this sleeve conductor overconductorLB and other contacts of the line-controller switches toprovide an idle-indicating test potential on the sleeve of the linkunless the link is in use. The busy or idle condition of the line linkserving primary switch 800B is separately indicated to block controller|600 over respective conductors in cable 222B.

IIIBB'?. Terminating-busy operation On testing the called line, if blockcontroller |6 iinds it busy, or nds that no idle path can be matchedthereto, the block controller grounds its terminating-busy lead TER-BU(shown in cable 22|), thereby operating busy relay el@ in the blockcoupler through contacts 'l of terminating-chain relay 5|8. Relay 5m, atits make contacts locks itself to ground on wire 56@ through breakcontacts 8 of sequence counter SE; opens its contacts 3 to release relay5|3 and to free the terminating chain; closes its contacts 5 to applybusy-tone current to the calling line from busytone wire BT through makecontacts E of relay 5% and tone-coupling condenser 52|.

If the calling subscriber does not replace his receiver in response tothe returned busy-tone signal to thereby cause the connection to becleared out normally, the connection is cleared out under 20 control ofthe common timing apparatus at the end of the normal time-out period, aswill hereinafter appear.

IIIBB8. Called-Zine seizure If the called line is idle, and if an idlepath can be matched thereto, block controller matches such a path, suchas over block link 206D. Fig. 3, terminating trunk 201B, and line-link202B.

As described, block-link 206U is selected mechanically at switches |380and Mll by the operation of select magnets 6M to 601, whereupon theycooperate to ground conductor SON to signal block controller |609.Line-link 202B is selected mechanically by the operation of selectmagnets SM-lll and SNI-104. Their circuit is closed at the blockcontroller over a wire in cable 222B, through line controller 12MB, wireLSM, a contact pair of one of the line-controller switches, theassociated select-magnet wire SM, and thence to battery through magnets104 and 105 in series.

With magnets 105 and 184 operated, a signal is transmitted to blockcontroller over 'a circuit path from battery at control resistor CR ofthe line controller |2llB series contacts of magnets 105 and 1M,contacts oi a line-controller switch, associated wire PS-ON, and thenceto the block controller over a wire in cable 222B.

Upon receiving the noted signals that the select magnets have operatedon the block-link and line-link frames, block controller ltll groundsthe sleeve of the called line 2|!) (Fig. Ll) over the noted testextensions thereof, thereby operating hold magnet HNL-193 in series withlockout relay Magnet 103 disconnects line relay 10| and connects thecalled line to the selected line link 202B. Block controller |600 alsogrounds the sleeve wire of the matched terminating trunk 201B (by way ofwire NIT-226) thereby operating magnet HMI-Glu on the block-link frameand secondary hold magnet HM-lt on the line-link frame. Block link 206Uis thereby extended over conductors T, R, and S of trunk 201B to linelink 282B. Block controller ll also grounds its switching wire TER-SW(shown in cable 22|), closing a circuit through contacts 8 of relay 5|6of block coupler 5ml and over conductor SW extending therefrom, tooperate the associated primary hold magnet HMZ- to complete theconnection over the matched path to the called line. Hold magnet HMZ-iZalso closes its local contacts to ground hold-pilot conductor HP whichoperates switching relay M3 through make contacts of tens register TR.

Upon operating, switching relay 513 opens its contacts 1 to restoreterminating-chain relay EIB and free the terminating chain and thecommon apparatus. Contacts t complete the operate path for ring-pickuprelay 591; contacts l0 open the impulse wire 55d to prevent furtherdialing; contacts .5 operate transfer relay 5|8 to disconnect the tenoutput leads of station register SR from station leads ST of the blocktranslator and transfer them respectively to the l0interruptor-generator leads INT-GEN to 9 and INT-GEN 0; contacts 2 and 3of relay 5 3* close the ringing circuit to the called line; contactslock relay 5|3 operated to the HP lead; contacts 9 remove ground fromthe make contacts of register SR in preparation for generator current tobe placed through these contacts to the calling line; and its contactsapply ringing-tone to the calling line from the common lead RT throughcontacts 5 of relay 5|2, contacts 6 of ring-cut-oi relay 5|0, makecontacts 6 0f relay 505 and through tone- The block couplers and theirassociated common ringing apparatus providefor accommodating up to tenharmoniceringing stations, `either `bridged or divided ringing, on anyparty line by (1) employing a one-ring code and` atwo-ring. code foreach of ve frequencies of ringing current, and by (2) ringing over oneline wire or the other according to the stationcalled, as shown in thefollowing ringing chart:

RIN GING. CHA RT Stations Digit Frequency 1 short on tip, Wire.

M The foregoing ringing arrangement provides: (l) Semi-selective(one-ring and two-ring) service for ten bridged stations(ringersibridged.

across the line) and (2) Full selective service for ten divided-ring-Iing `stations (the ringers of 1ring stations 0 to 4 connected betweenthe tip conductor and ground, and the ringers of 2-ring stations 5 to 9the ring conductor and ground). i,

In order to provide the foregoing party-line ringing service, teninterrupted-generator leads INT-GEN il to 9 are so controlled by theusual common ringing apparatus (not shown) that Nos. 0, l, 2, 3, and Ihave respective frequencies 1 to appliedthereto once during each ringingcycle, and,interrupted-generator leads Nos. 5to 9 have the respectivefrequencies 1- to 5 applied thereto twice `during each ringing cycle.

The ringing circuit is from` the selected one of the generatorleadsINT-GEN Il to INT-GEN 9, through the associated make contacts oftransfer relay 555, the associated contacts ofv station register SR,conductor 554, make contacts 2 of. ringpickup relay 50i, when operatedfrom ground on ring-pickup wire RI-PU and locked-to wire 5.60 throughcontacts I and contacts ilv of relay 510, and through the winding ofring-tip relay 508, to 1) the tip conductor T ofthe called line (ifstations digit l) to Il has been dialed, and ring-reverse relay 5t@ istherefore not operated) through break contacts 2 of relay 550 makecontacts 3` of relay 5 I 3, and break contacts I` of relay 5I00r (2) Ithe ring conductor R of the called line ofstations digit 5` to 9 hasbeen dialed and ring-reverse relay 509 is consequently operated, throughmake contacts I of relay 559,4make. contact 2 or relay 513, and breakcontacts 2 of relay 5'I0.

A return path for the transmitted ringing current is provided (l) overthe ring conductor R (when relay 500 is not operated) through` breakcontact 2 of relay 5I0, make` contacts 2 of switch relay 5I3 and throughbreak contacts I of relay 509, to generator ground conductor GEN-GRD or(2) over the tip conductor T (whenrelay 500 is operated) through breakcontacts I of relay 5.1.0, make contacts 3 of relay 5I,3 and makeycontacts 2 of relay 50e to conductor GEN-GRD.

l Ring-trip relay 50,8, whose Winding, isincluded 1n the ringing circuitdoes not operate before the 22?, calli is answered,` for-each ringer(not` shown) on the called linev has the usual condenser in seriestherewithto block direct current flow, and becauseA the shading collarsurrounding the armature endof the core of relay '500 keeps it from re-IIIBBlO. Ring-Catal? operation When thecall is'answered at the calledstation S2 on line ZIE, the closure of the usual talkingbridgeacross'thecalled line causes direct current to flow thereoverfromthe generator battery lead GEN-BATT to ground over the generatorlead (INT-GEN 0 to INT-GEN 9) in use, operating ring-trip relay 508.A Atits contacts I, :relay 508 places ground on the ring-cutoi relay 5I0thereby operatingit.

At, its contacts. I and 2, ring cut-off relay 5I0 opens the ringingcircuit and completes the talking circuit; its contacts 3 remove thelocking ground from ring-pickup relay 5cl permitting it torelease andAlocks ring-cutoff relay 5m operated; in addition to releasingring-pickup relay 507, it, also releases relays 509 and 5I8; itscontacts 4 open the operate circuit of ring-pickup relay 501 to preventits further operation; at its contacts 6 open the ring-tone lead RT toremove ringing-tone current; at its contacts 5, transfer they winding ofseries relay 5I I to time pulse lead TP', incidental to conversationtiming.

` IIIBBll. Answered supervision prevent normal time-out.

the following six relays of block coupler i500 are During conversation,(timing relays excluded) energized:

(1) Back-bridge relay 502 (2)` Line-relay 503 `(3) Hold-relay 504 (4)Hold-auxiliary relay 505 (5) Ring-cutoffY relay 5 I 0 (6) Switchingrelay '5I3 IIIBB12. Terminating-call clearout If the called subscriber(station S2, Fig. 4i) is; the rst to replace his receiver at the end ofthe conversation, back-bridge relay 502 thereupon restores, reversingthe current flow over the called line back to its normal direction,reconnecting relay 506 to start a new normal time-out period.

When` the receiver is replaced on the calling line, line relay503restores and (at its make contact I) open-circuits hold relay 5M,which restores` a. moment later, removing ground potential (at its makecontacts l) from the hold-auxiliary relay '.illli` permitting it torelease.

Relay 5.0.5 at its contacts 2, remove ground potential from sleeveconductor S of the established connection thereby clearing it out, bythe release of the primary and secondary` hold magnets 'w3 and 005 onthe calling line-link frame, primary and secondary hold-magnets 652` and6I@` on the block-link frame, and secondary and primary

